Distributor-type injector pump, for multi-cylinder compression-ignition internal combustion engines

ABSTRACT

A distributor-type fuel injector pump for an internal combustion engine has a rotary distributor member formed with two outlet passages communicating with a pump chamber and arranged to distribute fuel intermittently to successive fuel delivery apertures leading to respective engine cylinders, so that in each revolution of the distributor the pump delivers to each cylinder a principal fuel injection at the end of the compression stroke, preceded by a pre-injection. Automatic timing control means advance the delivery stroke of the pump automatically in response to engine speed increase, and the angle between the outlets of the two outlet passages is such that as the engine speed varies the ratio of the fuel pre-injected to that of the principal injection into each cylinder varies according to a rule predetermined in relation to the type of engine (i.e. precombustion chamber or direct injection type).

DESCRIPTION

The present invention relates to distributor-type injector pumps formulti-cylinder compression-ignition internal combustion engines.

In particular, the invention concerns injector pumps of the typecomprising: a pump body having an internal cylindrical cavity and acompression chamber; means for the introduction of fuel into the saidcompression chamber; piston means slidable within the body forcompressing fuel in the said compression chamber; a number of deliveryapertures in the wall of the cylindrical cavity of the body forcommunication with each of the cylinders of the engine; a rotarydistributor member located in the said cylindrical cavity; two distinctfuel passage means, formed in said rotary distributor member and eachhaving an inlet end permanently communicating with the compressionchamber and an outlet end in the external surface of the distributormember, the outlet ends of the said passage means being situated in twoareas angularly separated from each other such that they comeintermittently into communication, upon rotation of the distributormember, with the successive said delivery apertures to effect, incorrespondence with each fuel delivery stroke of the said piston means,two injections of fuel into two different cylinders of the engine, sothat the pump delivers into each cylinder of the engine in each cyclethereof a principal injection of fuel substantially at the end of thecompression stroke, preceded by a preinjection of fuel, and meanssensitive to the engine rotational speed for controlling the timing ofthe injection and adapted to advance the start of the delivery stroke ofthe piston means upon increase in the engine rotational speed.

As is already known, the purpose of the preinjection is to reduce thedelay in the ignition of the fuel introduced by means of the principalinjection. Such reduction in the said delay makes it possible toeliminate some difficulties characteristic of compression-ignitioninternal combustion engines: in the first place, the combustion noise isconsiderably reduced, and in the second place the reduction in theignition delay makes it possible to reduce the quantity of atmosphericpollutants (nitrogen oxide, carbon particles and carcinogenic compoundsabsorbed by the latter) present in the engine exhaust gases.

For satisfactory preinjection it is necessary that the quantity of fuelintroduced by preinjection should be sufficient to cause inside therespective cylinder of the engine an increase in temperature, due to thedevelopment of pre-burning reactions, such as to reduce the saidignition delay. If, however, this quantity of preinjected fuel exceeds afixed limit value, this would cause complete and untimely oxidation ofthe preinjected fuel with consequent strong pressure fluctuations withinthe cylinder and a reduction in the utilizable thermal efficiency.

Furthermore, in determining of the quantity of fuel to be introduced bypreinjection into each cylinder, account must be taken of the effect ofthe preinjection on the fuel consumption and on the quantity of unburnedhydrocarbons present in the engine exhaust gases.

Finally, the characteristics of the preinjection must be adapted to theparticular type of engine to be fed by the injection pump. Inparticular, the injection characteristics for an engine of theprecombustion chamber would be different from those for an engine of thedirect injection type: for an engine of the precombustion type injectionoccurs in the hot environment of the precombustion chamber, while for anengine of the direct injection type it is necessary to avoid the jet ofinjected fuel impinging directly on the cold walls of the cylinder,since this would impede complete combustion.

An injector pump of the type previously referred to is disclosed inFrench Pat. No. 1,218,469. By means of the pump described in this patentit is possible to effect preinjection by relatively simple means, butthe solution proposed in this patent does not solve the problem ofcontrolling the quantity of fuel preinjected in relation to therotational speed of the engine, and limiting the preinjection to engineoperation speeds at which it is advantageous and at which anydisadvantages as regards, for example, fuel consumption or unburnedhydrocarbons in the engine exhaust, are non-existent or negligible.Furthermore, this patent does not include any instruction for theadaptation of the preinjection to the different needs of different typesof engine.

Another known type of injector pump of the aforesaid type is disclosedin the following German Patent Applications published prior toexamination: DOS 1476215, DOS 1476216 and DOS 1476217. The injectorpumps described in these patent applications are equipped with means forcontrolling in dependence upon the engine load and the type of enginethe quantity of fuel preinjected relative to the quantity of fuelintroduced with the principal injection.

However, such control of the preinjection is independent of therotational speed of the engine, so that it is not possible to limit thepreinjection only to those engine speeds at which the preinjection isactually effective.

The object of the present invention is to provide an injector pump ofthe type previously defined by means of which it is possible to control,with extremely simple means which may be readily adapted to the type ofengine intended to be fed by the pump, the quantity of fuel preinjectedin such a way as to ensure the effectiveness of the preinjection asregards reduction of ignition delay, while substantially avoiding theattendant disadvantages such as increased fuel consumption and unburnedhydrocarbons in the engine exhaust gases.

With this object in view, the present invention provides an injectorpump of the distributor type previously referred to, characterised inthat the angle (α) between the outlet ends of the said two fuel passagemeans is so determined that, as the engine rotational speed varies, thesaid means controlling the injection timing causes a variation,according to a predetermined rule dependent on the characteristics ofthe engine to be fed by the pump, in the ratio of the quantity of fuelpreinjected into each cylinder in each engine cycle to the quantity offuel injected in the principal injection.

When the engine to be fed by the injector pump of the present inventionis of the precombustion chamber type, the said angle is selected suchthat the quantity of fuel preinjected into each cylinder in each cycledecreases as the speed of rotation of the engine increases, in such away that the said ratio becomes null for values of the engine rotationalspeed exceeding a threshold value substantially equal to half themaximum speed of rotation of the engine.

When the engine to be fed by the injector pump is of the directinjection type, the said angle is selected in such a way that thequantity of fuel preinjected into each cylinder in each cycle decreasesas the speed of rotation of the engine decreases in such a way that thesaid ratio becomes null for values of the engine rotational speed lessthan a threshold value substantially equal to half the maximum speed ofrotation of the engine.

The injector pump according to the invention will now be described, byway of non-limiting example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a diagrammatic longitudinal section of an injector pumpaccording to a first embodiment of the invention;

FIG. 2 is a cross-section taken on line II-II of FIG. 1;

FIG. 3 is a cross-section taken on line III-III of FIG. 1;

FIG. 4 illustrates diagrammatically a detail of the pump of FIG. 1 inone specific working condition;

FIG. 5 is a cross-section corresponding to FIG. 3 of a variant of thefirst embodiment;

FIG. 6 is a diagrammatic illustration corresponding to FIG. 4 of avariant of the first embodiment;

FIG. 7 is a longitudinal sectional view of an injector pump according toa second embodiment of the invention;

FIG. 8 is a cross-section taken on line VIII--VIII of FIG. 7;

FIG. 9 is a cross-section taken on line IX--IX of FIG. 7;

FIG. 10 illustrates diagrammatically a detail of the pump of FIG. 7 inone specific working condition;

FIG. 11 is a cross-section corresponding to FIG. 9 of a varient of thesecond embodiment, and

FIG. 12 is a diagrammatic illustration corresponding to FIG. 10 of avariant of the second embodiment.

The pump illustrated in FIG. 1 is intended to deliver fuel to afour-cylinder compression-ignition engine and comprises a fixed body 1having a cylindrical bore 2 within which a cylindrical distributormember 3 is rotatably housed. The distributor member 3 is rotatablydriven by means of a mechanical transmission, not shown, from the engineto which the injector pump supplies fuel. The distributor member 3 has atransverse cylindrical bore 4 in which two opposing pistons 5 slide.

A cam ring 6 co-axial with the distributor member 3 has an internal camsurface engaged by two cam-follower rollers 7 carried by the distributormember 3 and connected to the respective pistons 5. Upon rotation of thedistributor member 3 the cam ring 6 causes reciprocating movement of thepistons 5 in the bore 4. A compression chamber 5a is delimited withinthe bore 4 between the facing surfaces of the pistons 5.

The distributor member 3 is provided with an axial duct 8 whichcommunicates at one end with the compression chamber 5a, and which alsocommunicates with four radial ducts 9 in the distributor member 3,angularly equidistant from each other. Upon rotation of the distributormember 3 the ducts 9 are brought successively into momentarycommunication with a duct 10 formed in the body 1 of the pump andthrough which fuel is fed to the pump.

The distributor member 3 is also provided with two radial ducts 11, 12communicating at their radially inner ends with the axial duct 8 andhaving their radially outer ends situated in two zones of the externalsurface of the distributor member 3 separated angularly from each otherby an angle α (FIG. 3). Upon rotation of the distributor member 3 theducts 11, 12 are placed successively into momentary communication withfour delivery ports 13 formed in the cylindrical wall of the bore 2 andeach connected with a respective one of the cylinders of the engine, soas to effect into each cylinder of the engine a principal injection anda preinjection of fuel respectively in each cycle of the engine.

The said mechanical transmission by means of which the engine impartsrotary drive to the distributor member 3 is such that the said member 3makes one complete revolution for every two revolutions of the enginecrankshaft.

The value of the angle α is close to 180°, as illustrated in FIGS. 1 and3, or is close to 90°, as illustrated in FIG. 5, according to whetherthe engine to be fed is of the direct injection type or of theprecombustion chamber type respectively.

Where the engine to be fed by the injector pump is of the directinjection type, it is necessary to effect the preinjection into eachcylinder substantially at the end of the exhaust stroke, when the pistonis close to top dead-centre and prevents the preinjected fuel frommaking contact with the relatively cold walls of the cylinder.

Where, on the other hand, the engine is of the precombustion chambertype it is preferable to effect the preinjection into each cylindersubstantially at the beginning of the compression stroke.

The injector pump according to the invention is provided with means,known per se, (not shown) sensitive to the speed of rotation of theengine and adapted to advance the beginning of the active phase in whichfuel supplied to the pump through the duct 10 is compressed by thepistons 5. Such engine speed responsive means act on the ring 6, causingit to rotate with respect to the body 1 of the pump so as to vary theangular position of the distributor member 3 in each revolution thereofat which the pistons 5 are moved towards each other.

The operation of the pump illustrated in FIGS. 1 to 3 is as follows: fora given rotational speed of rotation of the engine, and therefore for agiven speed of rotation of the distributor member 3, the fuel is fedthrough the ducts 10, 9 and 8 to the compression chamber 5a. When theducts 9 cease to communicate with the duct 10 in the body of the pumpthe pistons 5 approach each other and force fuel under pressure throughthe ducts 8, 11 and 12 through diameterically opposed ports 13 into twodifferent cylinders of the engine in order to effect the principalinjection and the preinjection respectively.

Upon variation of the rotational speed of the engine the operation ofthe pump differs according to whether the engine is of the directinjection type or of the precombustion chamber type.

For a direct injection type of engine FIG. 4 illustrates, in developedplan, the relative angular positions of one of the delivery ports 13 andthe outlet end of the duct 12 at the start and at the end of the fueldelivery stroke of the pistons 5, for different rotational speeds of theengine. The direction of the relative movement of the outlet end of theduct 12 with respect to the delivery port 13 due to the rotation of thedistributor member 3 is indicated by an arrow in FIG. 4.

If the engine is running at idling speed, the outlet end of the duct 12is located, at the beginning and at the end of the fuel delivery strokeof the pistons 5, in the positions indicated by A and B respectively. Inthese conditions, then, preinjection is not effected, since the duct 12does not communicate with the port 13 during the fuel delivery stroke ofthe pistons 5.

When the rotational speed of the engine increases the ring 6 rotates soas to advance the delivery stroke of the pistons 5. At a certain speedof rotation of the distributor member 3 the outlet end of the duct 12 islocated, for example, in the positions indicated respectively by A₁ andB₁ at the beginning and at the end respectively of the delivery strokeof the pistons 5. Under these conditions the duct 12 and the port 13 arein communication with each other at the commencement of the deliverystroke so as to allow preinjection to be effected into the cylinderwhich is in communication with the said port 13.

The said angle α is so selected that the preinjection is effected onlywhen the engine rotational speed is greater than a threshold valuesubstantially equal to half the maximum speed of rotation of the engine.

FIG. 6 is a developed plan view corresponding to FIG. 4 for the variantshown in FIG. 5 for use with an engine of the precombustion chambertype. In this case, if the engine is at idling speed, the outlet end ofthe duct 12 is located in the positions indicated by C and D at thebeginning and at the end respectively of the delivery stroke of thepistons 5. Under these conditions preinjection is effected since theduct 12 and the port 13 are in inter-communication before the end of thesaid delivery stroke.

Upon increase in the engine rotational speed rotation, the ring 6rotates so that at a certain engine speed the outlet end of the duct 12is located, for example, in the positions indicated respectively by C₁and D₁ at the beginning and end respectively of the delivery stroke ofthe pistons 5. Under these conditions preinjection is no longer effectedsince at the end of the delivery stroke of the pistons 5 the duct 12 andthe port 13 are out of communication with each other.

In this case the angle α is such that the preinjection is effected onlywhen the speed of rotation of the engine is less than a threshold valuewhich is substantially half the maximum speed of the engine.

The required control of the fuel preinjection upon variation in theengine rotational speed in the case of a direct injection engine isdifferent from the preinjection control required for a precombustionchamber engine, due to the different combustion characteristics of thesetwo types of engine.

It will be evident from the preceding description that the selection ofthe optimum value of the angle α for operating the invention depends onthe geometry of the distributor and in particular on the diameter of thedistributor member 3, the diameter of the outlet end of the duct 12 andon the diameter of the delivery port 13.

Tests carried out on an injector pump of the type illustrated in FIG. 1based on the CAV (Trade Mark) pump type DPA, having a distributor member3 of 18 mm diameter, delivery ports 13 of 2.3 mm diameter, and a duct 12of 0.5 mm diameter have indicated the following optimum values of theangle α for the two different types of engine, having, in each case,four cylinders and a total cylinder capacity of 2500 cm³ :

Precombustion chamber engine: α=84°

Direct injection engine: α=186°

It will be understood that although the pump illustrated is intended tosupply fuel to a four-cylinder engine, it may readily be modified tofeed an engine with any number of cylinders.

In the second illustrated embodiment of the pump, illustrated in FIG. 7,which is also intended to supply fuel to a four-cylinder engine,components which correspond to those of the pump of FIG. 1 are indicatedwith the same reference numerals.

In the pump illustrated in FIG. 7 the pump has a rotary distributormember 3 which is slidable axially inside the cylindrical bore 2 in thepump body 1. The distributor member 3, as in the embodiment of FIG. 1 isrotatably driven by transmission means by the engine in which the pumpis mounted.

The axial displacement of the distributor member 3 is controlled by acam 14 fixed onto one end of the distributor member 3. The cam 14 has anaxially facing cam surface engaged by a roller 15 supported rotatably ona shaft 16 mounted upon a ring, not shown, co-axial with the rotarydistributor member 3. This pump is provided with known means, not shown,responsive to the speed of the engine, for advancing the beginning ofthe fuel delivery stroke of the pump. These means act on the ring whichsupports the roller shaft 16, rotating this ring with respect to thebody 1 so as to vary the angular position in each revolution of thedistributor member 3 at which the said member 3 is displaced axiallyupwardly, as shown in FIG. 7.

Also for this pump the value of the angle α by which the outlet ends ofthe ducts 11, 12 are separated is close to 180°, as illustrated in FIGS.7 and 9, or is close to 90°, as illustrated in FIG. 11, according towhether the engine to be fed by the pump is of the direct injection typeor of the precombustion chamber type.

In the pump illustrated in FIGS. 7 to 9 the ducts 9 are formed in theend of the distributor member 3 within the pump body 1 and enterintermittently into communication with the fuel supply duct 10 todeliver fuel to the compression chamber 5a. The ducts 9 compriseangularly equidistantly spaced longitudinal channels which communicatewith a compression chamber 5a within the bore 2 closed by the inner endof the distributor member 3.

The operation of the fuel injector pump of FIG. 7 is as follows: for acertain value of the speed of rotation of the engine and therefore for acertain value of the rotational speed of the distributor member 3, fuelis fed intermittently through the ducts 10 and to the compressionchamber 5a. When the ducts 9 and 10 are out of communication with eachother the distributor member 3 is displaced upwards, by the effect ofthe engagement of the cam 14 with the roller 15 during the rotation ofthe distributor member 3, causing fuel to be fed through the ducts 11and 12 and the delivery ports 13 into two different cylinders, to effectrespectively the principal injection in one cylinder and thepreinjection in the other cylinder.

Upon variation of the rotational speed of the engine, the action of thepump differs according to whether it is used on an engine of the directinjection type or of the precombustion chamber type.

FIG. 10 illustrates, in developed plan, the relative positions of one ofthe delivery ports 13 and the outlet end of the duct 12, at thebeginning A and at the end B respectively of the delivery stroke of themember 3 at different engine rotational speeds, in the case of thedirect injection type engine. The operation is in this case analogous tothat described with reference to FIG. 4, with the difference that now,because of the reciprocating movement of the distributor member 3, thetrajectory of the outlet end of the duct 12 is not rectilinear, butcurvilinear, as indicated by a broken line in FIG. 10.

FIG. 12 illustrates the variant of FIG. 10 corresponding to the case inwhich the engine intended fed by the pump is of the precombustionchamber type. In this case the operation of the pump is analogous tothat described with reference to FIG. 6, the sole difference being thatthe trajectory described by the outlet end of the duct 12 is curvilinearrather than rectilinear.

Tests carried out on an injector pump of the type illustrated in FIG. 7based on a Bosch pump of the EP/VE type, having a distributor member 3of 9 mm diameter, delivery ports 13 of 2.2 mm diameter, and a duct 12having a diameter of 0.6 mm, have established the following optimumvalues of the angle α for a four-cylinder engine having a total cylindercapacity of 2500 cm³, of the two types referred to:

Precombustion chamber engine: α=77°

Direct injection engine: α=193°

It will be understood that details of construction and practicalembodiments may be varied widely with respect to what has been describedand illustrated purely by way of example, without departing from thescope of the invention.

We claim:
 1. A fuel injection pump for a multi-cylindercompression-ignition internal combustion engine of the direct-injectiontype, said pump comprising:a pump body having an internal cylindricalcavity and a compression chamber, means for the introduction of fuel inthe said compression chamber, piston means slidable within the body forcompressing fuel in the said compression chamber, means defining anumber of delivery apertures in the wall of the cylindrical cavity ofthe body for communication with each of the cylinders of the engine, arotary distributor member located in the said cylindrical cavity, saiddistributor member being rotatable by drive transmitted from the enginein use of the pump to effect one complete revolution in said cavity ineach cycle of the engine, two distinct fuel passage means, formed insaid rotary distributor member and each having an inlet end permanentlycommunicating with the compression chamber and an outlet end in theexternal surface of the distributor member, the outlet ends of the saidpassage means being situated in two areas angularly separated from eachother such that they come intermittently into communication, uponrotation of the distributor member, with successive said apertures toeffect, in correspondence with each fuel delivery stroke of the saidpiston means, two injections of fuel into two different cylinders of theengine, so that the pump delivers to each cylinder of the engine in eachcycle thereof a principal injection of fuel substantially at the end ofthe compression stroke in said cylinder, preceded by a pre-injection offuel, means sensitive to the engine rotational speed for advancing thestart of the delivery stroke of the piston means upon increase in theengine rotational speed, wherein the angle between the outlet ends ofthe said two fuel passage means is such that when the engine rotationalspeed is lower than a threshold value substantially equal to half themaximum speed of rotation of the engine, only one of said two fuelpassage means communicates with one of said delivery apertures duringeach fuel delivery stroke of said piston means, whereby only theprincipal injection is delivered to each cylinder of the engine in eachcycle thereof when the rotational speed of the engine is lower than saidthreshold value.